Emit deprecation warning when 2to3 is used. Ref #2086.

setuptools/lib2to3_ex.py

@@ -7,6 +7,7 @@ Customized Mixin2to3 support:
 This module raises an ImportError on Python 2.
 """
 
+import warnings
 from distutils.util import Mixin2to3 as _Mixin2to3
 from distutils import log
 from lib2to3.refactor import RefactoringTool, get_fixers_from_package
@@ -33,6 +34,12 @@ class Mixin2to3(_Mixin2to3):
             return
         if not files:
             return
+
+        warnings.warn(
+            "2to3 support is deprecated. Please migrate to "
+            "a single-codebase solution or roll your own "
+            "conversion process.",
+            DeprecationWarning)
         log.info("Fixing " + " ".join(files))
         self.__build_fixer_names()
         self.__exclude_fixers()

setuptools/tests/test_test.py

@@ -73,7 +73,11 @@ def quiet_log():
     log.set_verbosity(0)
 
 
+ack_2to3 = pytest.mark.filterwarnings('ignore:2to3 support is deprecated')
+
+
 @pytest.mark.usefixtures('sample_test', 'quiet_log')
+@ack_2to3
 def test_test(capfd):
     params = dict(
         name='foo',
@@ -124,6 +128,7 @@ def test_tests_are_run_once(capfd):
 
 
 @pytest.mark.usefixtures('sample_test')
+@ack_2to3
 def test_warns_deprecation(capfd):
     params = dict(
         name='foo',
@@ -149,6 +154,7 @@ def test_warns_deprecation(capfd):
 
 
 @pytest.mark.usefixtures('sample_test')
+@ack_2to3
 def test_deprecation_stderr(capfd):
     params = dict(
         name='foo',